In an effort to optimize the operation of internal combustion engines, there have been numerous proposed improvements to cylinder valve designs. One approach has been to replace conventional valve assemblies with electromagnetically powered systems for moving engine valves. Electromagnetic valve actuators eliminate the need for the most complex and costly parts of the engine, namely the camshaft, drive gears, valvetrain components and emissions devices.
Referring to prior art FIG. 1, there is shown a known electromagnetic actuator 10. The actuator 10 includes two pairs of electromagnetic elements 12, a plurality of coils 14, a core 16, a support spring 20, a valve stem 22, and a valve case 24. Each of the electromagnetic elements 12 defines a central chamber 26. The central chamber 26 further defines a central vertical axis 28. Each pair of electromagnetic elements 12 further comprises an upper electromagnetic element 32 and a lower electromagnetic element 34. The upper and lower electromagnetic elements each include a central channel 30, in which the coils 14 are disposed. The upper and lower electromagnets 32, 34 are in a mirrored relationship to each other, with the central channels 30 of the upper and lower electromagnetic elements being in a facing relationship to each other.
Disposed intermediate the upper and lower electromagnetic elements 32, 34 is the armature element 16. The armature element 16 is interconnected to the valve stem 22. The valve stem 22 extends in axial alignment with the central vertical axis 28 of the central chamber 26 of the electromagnetic elements 12. A valve case 24 encloses the valve. The support spring 20 is disposed within the central chamber 26 surrounding the valve stem 22.
To close the valve, the upper electromagnet is energized, attracting the armature to the first electromagnet and compressing the upper spring. To open the valve, the energized first electromagnet is turned off and the second electromagnet is energized. Due to the force of the pre-stressed spring, the armature is accelerated toward the second electromagnet thereby reducing the amount of magnetic force required to attract the armature away from the upper electromagnet.
A problem with the use of electromagnetically actuated valves with modern internal combustion engines is that the design of engines only allows a specific area for the intake and exhaust valves. Because of the shape and height requirements of the known electromagnetic actuators, it is difficult to replace the camshaft-driven valves with electromagnetically actuated valves without requiring substantial modifications to some engine designs. Therefore, a need exists for an electromagnetic valve actuator assembly design that is compact and compatible with a modern automobile internal combustible engine, with minimal modifications to the engine design.
Another problem with prior electromagnetically actuated valves is in obtaining a zero gap at the upper electromagnet when the valve is properly seated. This problem is exacerbated by the thermal expansion of the engine and actuator materials that occurs during operation of the valve. The valve needs to be seated before the armature element reaches the upper electromagnet. Thermal expansion may prevent the armature from obtaining a zero or near zero gap. A zero or near zero gap is desired to maintain power consumption at a low level and failure to attain a near zero gap results in inefficient operation of the valve system. Therefore, it is desirable to have an electromagnetic actuator design that ensures that the armature element contacts the upper electromagnet after closure of the valve.
Another limitation of the previously designed valves is that the placement of the spring requires the existence of a central chamber. The upper and lower electromagnets each have a channel disposed therein to accommodate the support spring. The gap in the center of the electromagnet reduces the electromagnetic surface area available to attract the armature. Accordingly, it is desirable to have an electromagnetic actuator design that maximizes the electromagnetic surface area available for the actuation of the armature.
Another problem with the previously designed valves is that the moving armature element must return to an initial neutral position when not in operation. As previously described, it is known to use a spring to bias the armature element in this neutral position. However, spring tensions inevitably vary, which creates difficulty in obtaining a neutral position for the armature element that is biased between the upper and lower electromagnets. Therefore, it is desirable to have a means for manually adjusting the position of the armature element in order to achieve the desired biased position.
Another restriction of the prior valve design is that it limits the options available for the placement of a sensor. To derive the full benefit of the variable valve timing feature of electromagnetic valve actuators, the actuator is supplemented with a servo control system. The servo control system utilizes a sensor to track the position of the valve or armature at any given time. It is known to use sensors to detect the position of the valve. However, previous valve designs have been limited in the location available for the placement of the sensor. To measure the position of the armature, the sensor is usually placed between the upper and lower electromagnets. The placement of the sensor near the electromagnet, however, has several disadvantages. Most importantly, the magnetic field created by the electromagnets influences the accuracy of the sensor signal. Accordingly, it is desirable to have an electromagnetic actuator design that provides more alternatives for placement of the sensor.